A dry dock is a channel shaped to receive a maritime vessel (e.g. ship or submarine). The channel can be flooded to enable the vessel to enter. The channel can then be drained to expose parts of the vessel that are normally underwater. The dry dock is provided with a platform or other structure to support the vessel in the absence of water in the channel. A dry dock may be used for refitting or other types maintenance or testing, especially where it is desirable to have access to the undersurface (e.g. keel) of the vessel.
FIG. 1 shows side and end views of an example of conventional dock furniture 100 used to support a maritime vessel in dry dock. The dock furniture 100 comprise a support stack (also referred to herein as a support block) comprise a number of different components mounted on one another. At the base of the stack is a dock block 18, which may be referred to herein as a Type 1 dock block, which has a standard shape and structural properties. The dock block 18 is a reinforced concrete structure for with a steel top surface and side holes to provide access for a lifting tool (such as a forklift). Mounted on each dock block 18 is a pair of steel wedges 16 and a plurality of layers of timber 14 (typically oak) provided to ensure the stack has the required height. Each layer of timber may comprise a plurality of elongate planks that lie adjacent one another. A softwood capper layer 10 is on the top of the stack to provide a compliant surface for abutting the vessel.
In practice a vessel is supported on a plurality of the support stacks like those shown in FIG. 1.
When any vessel is docked, the support blocks on which she sits obstruct part of the keel, preventing access for survey and painting. The problem is normally solved with one of two approaches:
1. Providing two docking support configurations, i.e. two sets of different locations for the support blocks to contact the keel, which means that different parts of the keel are covered depending on the configuration used.
2. Removing a subset of the support blocks whilst the vessel is docked is used. For example, the docking support configuration may be arranged to permit up to a fifth of the support blocks to be removed at a time.
In the first approach, the docking of a vessel can be carried out in two phases. During the first phase, the vessel is positioned on the support blocks in a first configuration to permit work to take place on exposed parts of the bottom. For example, the exposed surface may be surveyed, blasted and painted. Phase one is complete when all the works in the exposed parts of the bottom have been finished. In phase two, the dock is flooded and the vessel repositioned on the support blocks in a second configuration. For example, the vessel may be fleeted forward by the distance of one block spacing. The dock is then drained again and the remainder of the bottom can be accessed. Phase two may not necessary occur immediately after phase one. For example, the second configuration may be used the next time the vessel is docked.
In the second approach, removal of a support block is done by extracting the steel wedges 16 from the top surface of the dock block 18, which then allows the layers of timber 14 to be dismantled. However, the wedges and the steel surfaces which they bear on corrode easily and over a short period of use the surfaces can become uneven due to flaking corrosion. This makes the wedges difficult to remove. When this happens, it is necessary to split out the wood whilst it is still under load. This can be a time consuming process.